Pulsed laser micro-deposition pattern formation

ABSTRACT

A method of forming patterns on transparent substrates using a pulsed laser is disclosed. Various embodiments include an ultrashort pulsed laser, a substrate that is transparent to the laser wavelength, and a target plate. The laser beam is guided through the transparent substrate and focused on the target surface. The target material is ablated by the laser and is deposited on the opposite substrate surface. A pattern, for example a gray scale image, is formed by scanning the laser beam relative to the target. Variations of the laser beam scan speed and scan line density control the material deposition and change the optical properties of the deposited patterns, creating a visual effect of gray scale. In some embodiments patterns may be formed on a portion of a microelectronic device during a fabrication process. In some embodiments high repetition rate picoseconds and nanosecond sources are configured to produce the patterns.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Ser. No. 12/400,438, entitled“Pulsed Laser Micro-Deposition Pattern Formation”, filed Mar. 9, 2009.U.S. Ser. No. 12/400,438 is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

This invention is related to pulsed laser deposition, and the formationof patterned materials therewith.

BACKGROUND OF THE INVENTION

When using a pulsed laser for patterned material deposition, methodsfall into two general categories: laser-induced forward transfer (LIFT)and laser-induced backward transfer (LIBT). The ablated material istransferred to the receiving substrate in the same direction with LIFT,or in a reverse direction relative to the incident laser with LIBT. InLIFT, a target film needs to be deposited on a laser-transparentsupporting substrate. The receiving substrate is placed facing thetarget film. The laser beam, incident from the uncoated side of thetarget supporting substrate, causes ablation in the target film. Theablated material is transferred forwardly in the same direction as thelaser, and to the receiving substrate. In a LIBT setup, the geometry isreversed. The laser is guided through the laser-transparent receivingsubstrate first and focused on the target. The target can be a platemade of the desired target material. Upon ablation, the ablated materialis transferred backwardly, in a reverse direction to the incident laserbeam, and deposited on the receiving substrate.

Several LIFT methods are disclosed in, for example, U.S. Pat. Nos.4,752,455 and 6,159,832 issued to Mayer, U.S. Pat. No. 4,987,006 issuedto Williams et al., U.S. Pat. Nos. 6,177,151 and 6,766,764 issued toChrisey et al. A few LIBT methods are described in U.S. Pat. No.5,173,441 issued to Yu et al, Japan patent 2005-79245 issued to Hanadaet al., and US patent application 2007/0243328 to Liu et al.

Laser-induced-plasma assisted ablation has been used for color markingof metal targets, as disclosed by Hanata et al, “Colour marking oftransparent materials by laser-induced-plasma-assisted ablation(LIPAA)”, Journal of Physics: Conference Series 59 (2007), 687-690.Various lasers were tested, and produced various picosecond, nanosecond,and femtosecond outputs, with a maximum repetition rate of 10 KHz. Forthis RGB process it was concluded that a conventional nanosecond pulsewidth has great potential for high-quality and cost effective marking inthe laser-marking industry.

An object of the above methods is precise and patterned deposition ofmaterials. If applied to printing, these methods are binary and wouldprovide an on/off effect or a visually black/white effect. In order toprint a bitmap image over a large gray scale range, two requirementsneed to be satisfied: (i) sufficient number of gray scale levels and(ii) a practically acceptable speed of printing.

A recent international patent application, WO 2008/091898 by Shah etal., assigned to the assignee of the present application, discloses amethod of ultrashort pulsed laser printing of images on solid surfaces.This method is based on surface texturing induced by ultrashort pulsedlaser interaction with solid surfaces. In a range of laser fluence andexposure time (average power per unit area), several types of surfacetextures can be produced after laser irradiation, including ripples,pillars, pores and many types of random micro-protrusions. A controlledarrangement of these textures produces a visual effect of gray scale byscattering, trapping, and absorbing light. This method does not involvematerial transfer from a target to a substrate.

LIFT, LIBT, and LIPAA systems have utilized Nd:YAG, Ti:Sapphire at a 1kHz repetition rate, and up to about 10 KHz with NdYVO₄ based systems.Forming patterns or images at high resolution on a macroscopic scalecould take up to a thousand minutes as a result of the low repetitionrates, limiting the application of these methods. Moreover, as set forthabove, many systems are limited to production of binary patterns.

SUMMARY OF THE INVENTION

An objective of one or more embodiments is precise deposition ofmaterials on transparent substrates, with both the location andthickness under control. The substrate may be a glass, or other suitablemedium.

At least one embodiment provides a LIBT method for forming a pattern ona transparent medium at a high speed.

In various embodiments the location and thickness of deposited materialis controlled to vary the optical density of a region of the medium suchthat a gray scale image is obtainable with illumination of the medium.By way of example, the location and thickness of deposited material iscontrolled over microscopic regions of the medium, and associatedvariations in reflectance over the medium create a visual effect of grayscale, and a discernible image when viewed with the un-aided eye, or atlow magnification. Either ambient or controlled illumination may beutilized.

In various embodiments a receiving substrate is placed adjacent andopposite to the target plate. A laser beam is guided through thereceiving substrate and is focused on the target such that the materialis ablated and transferred backwardly to the receiving substrate.

Another objective is laser printing of images, including but not limitedto artistic or photographic images, on transparent substrates. Moreparticularly, with a high repetition rate ultrashort pulsed laser, botha visual effect of gray scale and a fast printing speed can be achieved.

In various embodiments the gray scales are produced by varying materialdeposition such that the light transmission and reflection of theprinted patterns is varied depending on the thickness of the deposits.The thickness may be continuously controlled with control of laserparameters. A high repetition rate laser is utilized such that thetarget under the laser irradiation can receive a variable number oflaser pulses over a focused spot diameter.

In various embodiments the amount of deposition is varied in two waysduring printing: (i) varying the laser beam scan speed while maintaininga constant scan line density, (ii) varying the laser scan line densitywhile maintaining a constant beam scan speed. The first way provides forprinting bitmap images of art, photographs, and the like. The second wayprovides for printing vector graphics such as text patterns and simplegeometric figures.

Various embodiments provide fast printing speed. For example, in anembodiment with a laser repetition rate of 1 MHz, an image of 2×2 squareinch is printed in 20 sec to 1 min. With other lasers having 1 kHzrepetition rate, such a printing would take up to a thousand minutes.

In various embodiments PLD pattern formation may be carried out in air,and without a vacuum chamber. In some embodiments vacuum or some othercontrol of atmosphere may be utilized, for example gas flow of dry air.

The target materials can be metals, for example, steel, aluminum, orcopper. Steel will provide a brownish color to the printed image.Dielectric materials, including but not limited to silicon and carboncan also be used.

Another objective is to print patterns with a functional targetmaterial. Such a material provides special functions in addition tomodifying light transmission or reflection. In at least one embodiment,a target made of phosphor materials is used such that the printed imageis nearly invisible under room or sun light illumination, and only underspecial illumination with UV light, the image becomes visible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an arrangement for pulsed lasermicro-deposition pattern formation.

FIG. 2 schematically illustrates further details of an arrangement forpulse laser micro-deposition of materials to provide patterns of varyingoptical density.

FIGS. 3A and 3B show an example illustrating two optical microscopeimages of printed patterns.

FIGS. 4A and 4B show an example illustrating two images printed on2-inch glass wafers with a steel plate as the target.

FIGS. 5A and 5B show an example illustrating a text printed on a 1×1square inch glass wafer using a target made of a phosphor material.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a portion of an arrangement for pulsedlaser micro-deposition pattern formation, and provides an illustrationof laser-material interaction. In this example the laser beam 1 isdirected through a transparent medium 2, for example a glass substrate,and is focused on the target 3. Ablation removes materials at the focalpoint 4 and causes a small crater (not to scale). In this example theablated material, particularly the ejecta 5, transfers backwardly,generally propagating in a direction opposite to the laser incidentdirection. Material is deposited on the substrate, for example thesurface that is facing the target.

In at least one embodiment the substrate is positioned near the targetso that a small gap remains between the target and the receivingsubstrate 2. The gap width can be adjusted by inserting a spacer ofdifferent thickness between the substrate and the target. A small gapwidth is preferred, for example less than about 10 micrometers, toprovide high image resolution. In practice, the substrate may be placedin direct contact with the target. In such case, judging from theinterference fringes often appearing between a smooth target surface andthe substrate, the gap width is around 1 micrometer. In some embodimentsthe medium and target are spaced apart by a gap that provides separationThe gap may be filled with ambient air, or with flowing dry air. In someembodiment the gap may be filled with an inert gas, for example nitrogenor argon. Physical parameters, for example pressure, within the gap maybe controlled.

The interference fringes between the substrate and the target have highcontrast when the target surface is smooth and shiny. These fringes candegrade the quality of printing by modulating the laser fluence. One wayto avoid interference effects is to use a rough target surface, forexample a granular surface, to randomize the reflection off the target.In general, with a roughness greater than the laser wavelength theinterference effect can be reduced to negligible levels.

Referring again to FIG. 1, deposited material is heavily concentratednear the periphery of the beam scan line (not shown). A double line 6 isformed on the receiving substrate. This is because the high temperatureand high pressure under direct laser irradiation expels the ablatedmaterial sideways. Therefore, a localized region of the medium affectedby the laser interaction has a one-dimensional thickness profilecharacterizable by a central portion of low thickness bounded by thickerportions having controlled material deposition. By way of example, aresulting total line width of the deposition is about 2-3 times of thelaser focal spot size. With a laser spot size of 20 micrometer indiameter, the deposited line width is about 40-60 micrometer, yetsufficient for relatively high resolution image printing in variousembodiments.

FIG. 2 further illustrates an example of an arrangement for pulsed lasermicro-deposition of materials to provide patterns of varying opticaldensity. In this example, laser 7 is preferably a high repetition ratepulsed laser. A pulse selector, for example an acousto-optic orelectro-optic modulator (not shown), may be connected to controller 12and used to select pulses for delivery to the target. A beam scanner 8is used, under computer control, to form patterns. The scanner iscontrollable to produce varying scan speeds. Scanner 8 may comprise twoscanning minors 9 and 10, and a focal lens 11, for example an f-thetalens to provide a flat beam scan plane. A telecentric optical system maybe utilized in some embodiments. The scanner receives computerizedcontrol signals from the controller 12. A commercially available beamscanner system can be used, such as various products available fromSCANLAB America Inc., which includes a scan head, a controller with acomputer interface, and a user software to load images and edit textsand geometric figures.

In various embodiments other scan mechanisms may be utilized, alone orin any suitable combination, to form pre-determined spatial patternshaving varying optical density. For example, acousto-optic deflectors,polygons, rotating prisms, and the like may provide for further increasein scan speeds. Some embodiments may include a combination of fast andslow deflection mechanisms to control deposition while maintaining highscan speed. For example, a first scanning mechanism may scan at a fixedrate in a first direction, and a second scanner at a second rate in adirection opposite the first.

Various scan patterns may be generated, including trepanned or ditheredpatterns. Such mechanisms have been proposed and utilized in lasermarking, drilling, and micromachining, and may also be configured forpulsed laser micro-deposition pattern formation.

High repetition rate ultrashort lasers provide some benefits for PLDpattern formation. Compared with nanosecond pulsed laser ablation,ultrashort pulsed laser ablation requires less pulse energy to reachablation threshold. The available ultrahigh peak power with anultrashort pulse duration contributes to the low threshold. For example,a femtosecond pulse of a few micro-Joule has a higher peak power than aconventional nanosecond pulse of a few milli-Joule. Moreover, a reducedheat-affected zone (HAZ) at the focal spot significantly increases theenergy efficiency for ablation.

IMRA America Inc., the assignee of the present application, disclosedseveral fiber-based chirped pulse amplification systems which have ahigh repetition rate above 1 MHz, an ultrashort pulse duration from 500femtosecond to a few picoseconds, and a high average power of more than10 watts. Various fiber configurations are available commercially, asset forth below.

With a high laser repetition rate, for example in the range of 100 kHzto above 1 MHz, the target receives multiple laser pulses in a shorttime interval before the beam moves away from a localized focal region.For example, with 1 MHz repetition rate, a beam scan speed of 1 m/s, anda spot size of 20 micrometer in diameter, the number of overlappinglaser pulses is about 20, corresponding to about 95% overlap betweenadjacent spots. Multiple laser pulses with a close time separationbetween pulses, for example 1 microsecond or less, may produce physicaleffects to be considered for image formation. For example, (i)accumulation of deposition and (ii) accumulation of heat and pressure inthe air gap are of consideration. With a variable laser beam scan speed,the first effect produces different light transmission and reflectiondue to different deposit thickness, which is preferably controlled in acontinuous manner. The variation in thickness and associated changes intransmission and/or reflection creates a visual effect of gray scale.The second effect relates to the observation that the deposits areconcentrated near the periphery of the laser beam path, as illustratedin FIG. 1, and will be further illustrated with example images in FIG.3.

A high repetition rate pulsed laser is also needed for high printingspeed. Conventional solid state lasers such as Q-switched lasers andultrashort laser systems based on regenerative amplifiers providetypical repetition rates from 10 Hz to tens of kHz. Although about 20sec to 1 min is required to print a 2×2 square inch image with 1 MHzrepetition rate, approximately one thousand minutes are needed with arepetition rate of 1 kHz to have the same spatial overlap betweenpulses.

Various embodiments may utilize a fiber-based high repetition rateultrashort pulsed laser, for example a model FCPA μJewel made by IMRAAmerica Inc. The laser has a repetition rate from 100 kHz up to 5 MHz, apulse duration of 500 fs to 10 ps, and a pulse energy up to 20micro-Joule. With a focused beam spot of 20-30 micrometers in diameter,this laser can ablate many metals, dielectrics, and semiconductormaterials.

Operation at higher repetition rates is possible. U.S. provisionalapplication U.S. 61/120,022, entitled “Highly Rare-Earth-Doped OpticalFibers for Fiber Lasers and Amplifiers” to Dong et al., is incorporatedherein by reference. Various examples disclosed in the '022 applicationinclude highly rare earth doped gain fibers having pump light absorptionof up to about 5000 dB/m, and gain per unit length in the range of 0.5-5dB/cm. Various dopant concentrations reduce Yb clustering therebyproviding for high pump absorption, large gain, with low photodarkening.Such rare-earth doped fibers provide for construction of short cavitylength fiber lasers, and for generation of high energy ultrashort pulsesat a repetition rate exceeding 1 GHz. With availability of a GHz fibersource having increased pulse energy, an improved figure of merit can beobtained based on various combinations of pulse width, energy, spotsize, and average power, and preferably with the use of an all-fibersystem.

In various embodiments a repetition rate may be increased with acombination of beam splitter and optical delay lines.

FIGS. 3 and 4 illustrate the visual effect of gray scale. FIG. 3 showstwo microscopic portions with different gray levels taken from theprinted artistic image shown in FIG. 4( a). In FIG. 3( a), the twobright lines are made by a fast beam scan with a scan speed of 8-10 m/s.Referring back to FIG. 1, the deposited material 6 corresponds to theregion corresponds to the region between the bright lines in FIG. 3 a.As explained above, the whiteness of the scan lines is due to the hightemperature and high pressure under the direct illumination of the laserbeam, which forces the ejecta sideways. In FIG. 3( a), because of thefast scan speed, relatively few deposits remain, particularly on the topof the image.

FIG. 3( b) shows three scan lines made with a slow scan speed of 0.2 m/son average, where much thicker deposits formed between the lines,resulting in an overall visual effect of darkness. The white scan linesare also present. Therefore, different beam scan speeds control materialdeposition between the scan lines and produce the gray scale variation.In this way, a famous artistic image is printed and shown in FIG. 4( a).A nickel coin is placed beside the glass wafer to indicate thedimension.

In the above example, the number of gray levels is determined by theminimum increment of the beam scan speed and the maximum scan speed,assuming a linear dependence of deposit thickness with beam scan speed.For example, with a maximum scan speed of 10 m/s and an increment ofspeed of 1 mm/s, the increment of the amount of deposit is sufficientlysmall to produce a visually continuous gray scale.

FIG. 4( b) shows images of three identical text patterns with differentgray scales. In this example the patterns were formed by controllingscan line density while maintaining a constant beam scan speed of 5 m/s.For the three images from the top to the bottom, the scan line densitiesare 4, 8, and 12 lines per millimeter, respectively. This is an exampleof printing vector graphics. This pattern formation technique is alsosuitable for filling simple geometric shapes. By varying the scan linedensity, the available number of gray levels can exceeds 10. In variousembodiments an optical density (O.D.) of at least 1 unit (10:1) may beprovided, and up to about 3-4 units.

In various embodiments patterns are formed using materials providingfunctions other than changing the reflection or transmission of light.One example is shown in FIG. 5, where text is printed on a 1×1 squareinch glass wafer with a target made of a phosphor material. Thismaterial is a white powder under room or sun light, but with UVillumination, the material emits orange luminescence. Using thismaterial as the target, the printed text in FIG. 5( a) is barely visibleunder room light. In FIG. 5( b), with UV illumination, the text becomesbrightly luminescent. This demonstrates that the light emitting propertyof the original target material is preserved during printing.

In the above implementation, special physical and chemical functions ofthe target material are preserved, such as phosphorescence orfluorescence properties. Related physical and chemical properties of theoriginal material are not destroyed by laser ablation, although thematerial is disintegrated with laser irradiation. Ultrashort pulsesprovide such benefits.

Without subscribing to any particular theory, the process of pulsedlaser ablation can generally be separated into several stages, including(i) light absorption, (ii) heating and phase transition, and (iii)plasma expansion. The final material deposition strongly depends onlaser parameters including pulse duration, pulse energy, wavelength, andrepetition rate, and also on the types of target materials, for examplemetals or dielectrics. Among these factors, pulse duration is the firstto consider and compare between a conventional nanosecond pulsed laserand an ultrashort pulsed laser, because of the large difference ofseveral orders of magnitude.

With a nanosecond pulsed laser such as a Q-switched Nd:YAG, Nd:YLF, orNd:YVO₄ laser, the pulse duration is longer than the time scale ofenergy exchange between electrons and ions in a solid. The time scale istypically a few tens of picoseconds. The nanosecond laser pulsethermally heats the solid and results in thermal evaporation andionization, and a plasma is formed by the laser. The tail of the laserpulse can also further heat up the plasma, resulting in a nearlycompletely atomized and highly ionized vapor plume, except for a fewlarge liquid droplets. In the presence of the ambient air, a strongchemical reaction, e.g., oxidation, is expected during ablation, whichwill change the physical and chemical properties of the ablatedmaterial.

With an ultrashort pulsed laser having a pulse duration in the range ofseveral hundred femtoseconds to a few tens of picoseconds, and with alaser fluence within a range near the ablation threshold, the ablatedmaterial can disintegrate into small particles. Such particles may be inthe nanometer range, as reported in references No. 1-6 listed below.Several original physical and chemical properties are maintained, suchas crystallinity, chemical composition, and alloy composition, asreported in references No. 1-3. Thus, functional properties may beretained. Some examples of functional properties are phosphorescence,electro-luminescence, and selective light absorption and emission forvisual color effects. As illustrated in the example of FIG. 5, suchproperties may be exploited for PLD based microdeposition and patternformation.

Many possibilities exist for high-repetition rate sources suitable forPLD pattern formation. Ultrashort pulses and various configurationsdisclosed above provide for precise and repeatable material removal.However, in various embodiments a high repetition rate picosecond ornanosecond source may be utilized. It is known that the effectiverepetition rate of q-switched sources may be increased by splitting andrecombining outputs and/or combining multiple laser outputs. Forexample, a q-switched laser may have a base repetition rate of 70 KHzthat is increased to well over 100 KHz with the multiple lasers and/orsplitting and combining. Moreover, semiconductor laser diodes mayproduce picosecond or nanosecond pulses, and the diodes can be modulatedat very high repetition rates, at least tens of MHz. An output of thediode may be amplified with a fiber amplifier to increase the energylevel of picosecond or nanosecond pulses to the range of microjoules,for example. Pulse selectors may be used to gate pulses foramplification and delivery to the target. Many possibilities exist.

In various embodiments a metal target will be ablated, and various laserparameters may be pre-selected to control speed and resolution. By wayof example, pulsed laser micro-deposition pattern formation may becarried out with pulse widths less than 100 ns, and preferably below 10ps, at a repetition rate of at least about 100 kHz and much higher.Pulse energy below about 20 μJ provides a fluence of at least about 2.8J/cm² in a focused spot diameter of about 30 μm, and suitable forforming various patterns. The fluence is substantially greater than anablation threshold of many metals. Smaller spot diameters may beutilized. For a given fluence, the required energy decreases with spotarea, providing for a potential increase in repetition rate for a givenaverage power, but increased time for scanning. In various embodimentsmaterial deposition may be carried out with fluence near the ablationthreshold of a metal target.

Thus the inventors have described methods, systems, and a materials forpulsed laser micro-deposition and pattern formation.

At least one embodiment includes a method of pulsed laser deposition toproduce a pattern on a medium, the medium being substantiallytransparent at a wavelength of the pulsed laser. The method includesgenerating pulsed laser beams from a pulsed laser source, and focusingthe pulsed laser beams onto a target. The target produces ejecta inresponse to an interaction of the pulsed beams and the target. Themethod includes accumulating at least a portion of the ejecta on themedium to form material deposits on the medium. The method includescontrolling thickness of the material deposits to vary an opticaldensity of a region of the medium, and to form a spatial pattern havingvarying optical density.

In various embodiments:

the method includes transmitting the pulsed laser beams through themedium; scanning the laser beams relative to the medium and target; andvarying at least one of a laser beam scan speed and scan line density tocontrol the thickness.

at least a portion of the pattern is characterizable with aone-dimensional thickness profile having a central portion of lowerthickness than an immediately adjacent surrounding portion, thethickness of surrounding portion being controlled to vary the opticaldensity.

-   -   a pulsed laser source has a repetition rate from about 100 kHz        to 100 MHz, and up to about 1 GHz.    -   a laser pulse has a pulse duration in the range of about from        about 10 femtosecond up to about 100 nanosecond.    -   a laser pulse energy is in the range of about 100 nano-Joule to        about 100 micro-Joule.    -   a medium comprises glass, quartz, sapphire, plastic sheets, or a        polymer.    -   a target comprises a metal, and the metal may comprise steel,        aluminum, copper, gold, silver and/or platinum.    -   a target comprises a non-metal, and the non-metal may comprise        carbon, silicon, and/or organics materials such as a polymer.    -   a target comprises a functional material for emitting light, the        function comprising one or more of phosphor luminescence and        electro-luminescence.    -   a target comprises a material for color printing.    -   a target comprises a structure made of a target material.    -   a target material is a metal, and the metal may comprise a        precious metal.    -   a target material comprises a dielectric, and the dielectric may        comprise a mineral and/or metal oxide.    -   a laser beam scan speed is varied according the gray scale of        the pattern to be printed.    -   a laser beam scan speed of 1 mm/s-1 m/s is used to produce        accumulated deposition of material.    -   a laser beam scan line density is in a range of 1-100 lines per        millimeter.    -   a medium is placed in contact with the target, placed within 100        micrometers to the target, or placed within 5 mm to the target.    -   an optical density corresponds to at least three gray levels in        a digitized image of the pattern.    -   a target has a surface with a roughness greater than the        wavelength of the laser.    -   a pattern comprises a bitmap image and/or a vector graphic.    -   a grey scale image having a discernible feature is obtainable        with ambient or controlled illumination of the pattern.

a medium is disposed between the source and the target, and ejectapropagates in reverse to the laser direction.

controlling comprises scanning the pulsed beams and varying the scanspeed.

controlling comprises scanning the pulsed beams and varying the linedensity of the scan.

a medium is positioned relative to the target in such a way to controlthe spatial resolution of the pattern.

controlling comprises scanning the pulsed beams in one or more of araster and vector pattern over the target.

at least one pulse width is in the range of about 100 fs to about 10 ps.

At least one embodiment includes a system for pulsed laser deposition toproduce a pattern having optical density on a medium, the medium beingsubstantially transparent at a wavelength of the pulsed laser. Thesystem includes a high-repetition rate laser source for generatingpulsed laser beams, and a beam delivery system. The beam delivery systemincludes a focusing sub-system to focus the pulsed laser beams onto atarget, the target producing ejecta in response to an interaction of thepulsed beams and the target. At least a portion of the ejecta areaccumulated on the medium and form material deposits on the medium. Acontroller is coupled to the source and the beam delivery system forcontrolling thickness of material deposits to vary an optical density ofa region of the medium. A spatial pattern having varying optical densityis formed.

In various embodiments:

a delivery system comprises a beam deflector, and the focusingsub-system comprises a scan lens.

a controller is configured to vary at least one of a laser beam scanspeed and scan line density to control thickness.

the medium and target are spaced apart by a gap that providesseparation, and the gap may be filled with ambient air, or with flowingdry air, or an inert gas, for example nitrogen or argon. Physicalparameters, for example pressure, within the gap may be controlled.

At least one embodiment produces a product, including a medium having apattern formed thereon. The pattern is formed with a pulsed laserdeposition method described above. In various embodiments a patterncorresponds to a gray scale image having at least three detectable graylevels in a digitized image.

At least one embodiment includes a method of pulsed laser deposition toproduce a pattern on a medium, the medium being substantiallytransparent at a wavelength of the pulsed laser. The method includesgenerating pulsed laser beams from a pulsed laser source, and focusingthe pulsed laser beams onto a target. The target produces ejecta inresponse to an interaction of the pulsed beams and the target. Themethod includes accumulating at least a portion of the ejecta on themedium to form material deposits on the medium. The deposited materialcomprises a functional material that is operable to emit radiation inresponse to a stimulus. The method includes controlling thickness of thematerial deposits to vary an optical property of the material deposits.

In various embodiments an optical property of the functional materialcomprises one or more of phosphorescence, electro-luminescence, andselective light absorption and emission for visual color effects. Thestimulus may comprise radiation, for example short wavelength radiationthat causes fluorescence excitation.

Thus, while only certain embodiments have been specifically describedherein, it will be apparent that numerous modifications may be madethereto without departing from the spirit and scope of the invention.Further, acronyms are used merely to enhance the readability of thespecification and claims. It should be noted that these acronyms are notintended to lessen the generality of the terms used and they should notbe construed to restrict the scope of the claims to the embodimentsdescribed therein.

PUBLICATIONS REFERENCED

-   1. B. Liu et al., Appl. Phys. Lett. 90, 044103 (2007).-   2. B. Liu et al., Proc. SPIE 6460, 646014 (2007).-   3. B. Liu et al., Laser Focus World, 43, 74 (2007).-   4. S. Eliezer et al., Phys. Rev. B 69, 144119 (2004).-   5. S. Amoruso et al., Phys. Rev. B 71, 033406 (2005).-   6. T. E. Itina et al., Proc. of SPIE, 6458, pp 64581U-1 (2007).

What is claimed is:
 1. A method of pulsed laser deposition to produce a pattern on a medium, said medium being substantially transparent at a wavelength of said pulsed laser, said method comprising: generating pulsed laser beams from a pulsed laser source; transmitting said pulsed laser beams through said medium; focusing said pulsed laser beams onto a target, said target producing ejecta in response to an interaction of said pulsed beams and said target; scanning said laser beams relative to said medium and target; accumulating at least a portion of said ejecta on said medium to form material deposits on said medium; and varying at least one of a laser beam scan speed and scan line density for controlling thickness of said material deposits to vary an optical density of a region of said medium, and to form a spatial pattern having varying optical density, wherein said laser beam scan speed or said scan line density is varied according the gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.
 2. The method of claim 1, wherein said interaction causes sufficiently high temperature and pressure to expel ejecta sideways relative to said scan direction and to concentrate ejecta toward the periphery of the path of said laser beams such that the material deposits are formed with central low thickness portions bounded by immediately adjacent, thicker outer portions, and wherein said medium and said target are spaced apart by a gap, or are in direct physical contact, and the thickness of said deposits is controlled with a repetition rate and said scan speed of said laser beams.
 3. The method of claim 1, wherein said pulsed laser source provides a repetition rate from about 100 kHz to 1 GHz, a laser pulse having a pulse duration in the range from about 10 femtosecond up to 100 nanosecond, and a laser pulse energy in the range from about 100 nanoJoules (nJ) to about 100 microJoules (μJ).
 4. The method of claim 1, wherein said medium comprises glass, quartz, sapphire, or a polymer.
 5. The method of claim 1, wherein said target comprises a metal.
 6. The method of claim 1, wherein said target comprises a functional material for emitting light, said function comprising one or more of phosphor luminescence and electro-luminescence.
 7. The method of claim 1, wherein said target comprises a material for color printing.
 8. The method of claim 1, wherein said laser beam scan speed is in the range from about 1 mm/s to about 1 m/s, and utilized to produce accumulated deposition of material.
 9. The method of claim 1, wherein said medium is placed in contact with said target, or at a distance up to about 5 millimeters from said target.
 10. The method of claim 1, wherein said target has a surface with a roughness greater than an output wavelength of said laser source.
 11. The method of claim 1, wherein said pattern comprises a bitmap image or a vector graphic.
 12. The method of claim 1, wherein a grey scale image having a discernible feature is obtainable with ambient or controlled illumination of said pattern.
 13. The method of claim 1, wherein said medium is disposed between said source and said target, and said ejecta propagates reversely to the laser incidence direction.
 14. The method of claim 1, wherein said controlling comprises scanning said pulsed laser beams, and varying said scan speed.
 15. The method of claim 1, wherein controlling comprises scanning said pulsed beams and varying the line density of said pulsed beam scan.
 16. The method of claim 1, wherein controlling comprises scanning said pulsed beams in one or more of a raster or vector pattern over said target.
 17. A system for pulsed laser deposition to produce a pattern having optical density on a medium, said medium being is substantially transparent at a wavelength of said pulsed laser, said system comprising: a high repetition rate laser source for generating pulsed laser beams; a beam delivery system, comprising: a focusing sub-system to transmit said pulsed laser beams through said medium and to focus said pulsed laser beams onto a target; said target producing ejecta in response to an interaction of said pulsed beams and said target, accumulations of said ejecta forming material deposits on said medium; and a controller coupled to said source and said beam delivery system and controlling thickness of said material deposits to form a spatial pattern having varying optical density, by controlling scanning of said laser beams relative to said medium and target such that at least one of a laser beam scan speed and scan line density is varied, and wherein said laser beam scan speed or said scan line density is varied according to the gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.
 18. The system of claim 17, wherein said delivery system comprises a beam deflector, and said focusing sub-system comprises a scan lens.
 19. The system of claim 17, wherein said medium and said target are spaced apart by a gap providing separation, and said gap is configured to contain ambient air, flowing dry air or an inert gas.
 20. The system of claim 17, wherein said medium and said target are in direct contact.
 21. The system of claim 17, wherein the material deposits have central low thickness portions bounded by immediately adjacent, thicker outer portions, and wherein said medium and said target are spaced apart by a gap, or are in direct physical contact, and wherein said controller further controls a repetition rate of said pulsed laser beams and controls thickness of said deposits with said repetition rate and said scan speed of said laser beams.
 22. A method of pulsed laser deposition to produce a pattern on a medium, said medium being substantially transparent at a wavelength of said pulsed laser, said method comprising: generating pulsed laser beams from a pulsed laser source; transmitting said pulsed laser beams through said medium; focusing said pulsed laser beams onto a target, said target producing ejecta in response to an interaction of said pulsed beams and said target; scanning said laser beams relative to said medium and target; accumulating at least a portion of said ejecta on said medium to form material deposits on said medium, said deposits comprising a functional material that is operable to emit radiation in response to a stimulus; and varying at least one of a laser beam scan speed and scan line density for controlling thickness of said material deposits to vary an optical property of said material deposits, and to form a spatial pattern having varying optical density, wherein said laser beam scan speed or said scan line density is varied according to a gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.
 23. The method of claim 22, wherein an optical property of said functional material comprises one or more of phosphorescence, electro-luminescence, and selective light absorption and emission for visual color effects.
 24. The method of claim 22, wherein said stimulus comprises input radiation.
 25. A medium having a pattern formed thereon, said medium comprising material deposits formed, over microscopic region(s), with central low thickness portions bounded by immediately adjacent, thicker outer portions, said material deposits of said pattern providing for discernible images when viewed by the unaided eye or at low magnification.
 26. The medium of claim 25, wherein said pattern is viewed with ambient illumination.
 27. The medium of claim 25, wherein said pattern is viewed with controlled illumination.
 28. The medium of claim 25, wherein said pattern is formed with the pulsed laser deposition method of claim
 1. 29. The medium of claim 25, wherein said pattern is formed with the pulsed laser deposition method of claim
 22. 